1. Raw material of synthetic paper The performance of synthetic paper has a great relationship with the raw materials selected, and the choice of raw materials is related to the manufacturing method.

(1) Main raw material-synthetic resin

What kind of resin is used as the raw material to produce synthetic paper should be considered from the aspects of processing suitability, characteristics and price. Generally, general resins such as polyethylene, polypropylene and polyvinyl chloride are used. Other resins are less used due to higher prices, but polyester, nylon and other resins are also used to produce some spunbond synthetic paper or surface coated synthetic paper.

(2) Auxiliary materials

The auxiliary materials needed for synthetic paper include fillers, pigments and other additives.

Fillers or pigments for synthetic paper include calcium carbonate, barium sulfate, clay, talc, titanium dioxide, silicic acid, diatomaceous earth, etc. In order to make synthetic paper have "paper properties", that is, meet the requirements in terms of whiteness, opacity, printability and writing, the indicators of whiteness, particle size, refractive index, shading ability, stability, etc. Both are important, but also consider the price factor.

The adhesive used in synthetic paper for surface coating is basically the same as the adhesive used in general composite paper. Synthetic rubber latex and vinyl acetate latex are commonly used.

2. Synthetic paper manufacturing process

Different types of synthetic paper have different manufacturing processes.

(1) The manufacturing process of thin film synthetic paper

â‘ Inner papermaking method Synthetic paper first mixes the selected synthetic resin and filler, and adds appropriate additives such as stabilizer and dispersant. After fully mixed, it is loaded on an extruder and melt-kneaded. The molten material is then extruded from the slit of the T-die to form a film. There are generally two methods of film formation used in the production of synthetic paper.

a. Non-stretching film forming method This method is to thin the thin molten film extruded from the slit of the T-shaped die, cool and solidify into a film at the same time during the drawing process, and then take up. The cooling method can be different. One is that the outflowing molten film flows around the chrome-plated metal cooling drum, and is quenched and shaped, trimmed, and then wound up; the molten film can also be introduced into cooling water or other liquids for rapid cooling and shaping, and then removed. Trimming and winding.

b. Bidirectional stretch film forming method This method first extrudes a thick molten film from the T-die with an extruder, after cooling it becomes the stretched original sheet, and then heats the original sheet to the softening temperature in both longitudinal and horizontal directions Stretch film formation. Stretching is divided into two steps and one step, which is basically the same as the stretching of plastic films. The synthetic paper produced by the two-way stretching method can be divided into synthetic paper with micropores on the surface and synthetic paper without micropores. The former can improve the acceptability of ink, reduce the density and reduce the cost.

Compared with the unstretched film forming method, the production line of the biaxial stretch forming method is larger (however, it is much smaller than the paper production line of natural fiber paper). Therefore, the equipment investment is larger. However, after bidirectional stretching, the orientation of the randomly arranged polymer molecules becomes more regular. Generally, after orientation treatment, the arrangement of polymer molecules is parallel to the surface of the film, which improves the strength and rigidity of the paper.

Due to the continuous production line used to produce synthetic paper by internal papermaking, the production cost is lower. The Japanese エ ポ synthetic paper introduced earlier was produced by this method. The main raw material is polypropylene, and some fillers and small amounts of additives are added.エ ポ Whether synthetic paper is thick or thin, it has a three-layer structure. The filler content of the middle base layer is lower than that of the two surface layers, so it is closer to the properties of plastics. After the biaxially oriented film forming method is used for longitudinal and transverse stretching orientation, the mechanical properties such as strength and rigidity of synthetic paper are improved. At the same time, due to the high filler content, the two surface layers form a large number of fine pores in the stretching process and become a paper-like layer. Because these large number of fine pores can scatter light, improve whiteness, opacity, printability and writing, etc., which gives the paper properties. In addition, due to the low density and low grammage, the unit consumption of materials is low.

â‘¡ Surface paper-making method Synthetic paper uses synthetic resin film as the base material, and chemical treatment, physical treatment, or surface coating treatment is performed on the surface to make the synthetic resin film paper.

a. Surface chemical treatment method This method is suitable for polystyrene films, because it is easily affected by solvents. When it is to be paperized, a chemical liquid is applied on the surface of the film to partially dissolve or swell it, and many fine pores are generated after the chemical liquid evaporates. These fine pores scatter light, give whiteness and opaque appearance, improve ink acceptance and writing, etc., to achieve the purpose of paper-like. However, there is little production of synthetic paper in this way.

b. Surface physical treatment method This is to perform sandblasting and abrasion processing on the surface of hard plastic, so that the surface produces countless fine marks and unevenness, so as to impart writing and opacity. The base material is usually films such as polyethylene and cellulose acetate. The printability after processing in this way is poor, and its use is limited. In addition, in a broad sense, although the products produced by this method can be counted as synthetic paper, they are usually not called "synthetic paper".

C. Surface coating method This method, like ordinary coated paper, coats a layer of white pigment on the surface of the plastic film to give the film whiteness, writing properties, and ink absorption. The coating substrate is a film of resins such as polystyrene, polyvinyl chloride, polyester, etc., and synthetic paper made by other methods is often used as a substrate for surface coating. The method is simple in principle, but when formulating the coating, the adhesion to the substrate must be taken into consideration, as well as the water resistance. Unlike the production of ordinary coated paper, it is coated on non-absorbent materials, and the operation is relatively difficult.

(2) Manufacturing process of fiber-based synthetic paper

â‘  Spunbond synthetic paper has been mentioned before, usually, people categorize it as "non-woven fabric". The so-called spunbond method is to pass the resin stock solution through countless nozzles to form a fiber web while spraying yarn, and then impregnate and fix the fiber web with resin. The fiber network can also be mechanically combined to make spunbond synthetic paper. This method is very productive.

â‘¡Synthetic pulp method first is to prepare synthetic pulp. In order to prevent raw materials from fibrillating in water, short fibers of about 5 to 10 mm are generally used. The main raw materials are special short man-made fibers and synthetic fibers, and some natural fiber pulp is usually mixed. Then it can be made by traditional paper machine. Now special machines are also used to make products made from longer fibers. As mentioned earlier, this kind of product is generally called synthetic fiber paper, and it is also called wet non-woven fabric. [next]

3. Secondary processing of synthetic paper

(1) Cutting

Synthetic paper can be cut with a slitter or guillotine cutter. However, it should be noted that as long as there is a gap in the synthetic paper, it is easy to split from the lateral direction (direction of the grain flow), so it should be as sharp as possible.

(2) Printing

â‘  Lithographic offset synthetic paper is fundamentally different from ordinary paper in that it hardly penetrates the fountain solution and ink. Therefore, despite the same printing conditions, it is necessary to pay attention to the following three points:

a. Use special ink for synthetic paper;
b. Reduce the amount of water absorption (ethanol can be added through the fountain solution, etc.);
C. Due to the slow drying of the ink, it is best to use a multi-color printing machine, add a drier, spray a little more powder, and feed the plate after the ink is injected and improve the air.

â‘¡The printing conditions of gravure printing and flexographic printing are almost the same as that of ordinary plastic film printing. Because synthetic paper is not easy to generate static electricity and the applicable ink range is wide, it is much easier to print than plastic film.

Compared with the printing of ordinary paper, the following items should generally be noted:
a. To reduce tension;
b. It can be dried with hot air, but it should be noted that the paper temperature does not exceed 80 ℃;
C. All inks are available, but when using PVC-based inks, a fixed coating such as isocyanate must be used;
d. The printing speed is usually (50 ~ 150) m / min. When the climate is dry, static elimination devices must be used for high-speed multi-color printing.

â‘¢The general printing method of stencil printing can be printed, but pay attention to the selection of printing ink and use non-petroleum soft solvents.

â‘£Letterpress printing can be printed in the usual way, but lithographic offset printing ink should be used.

(3) Fold

The folding endurance of synthetic paper is excellent. Due to the high resilience of the crease, the paper discharge operation is more difficult than ordinary paper, and it is not stable after the paper discharge. Generally, it can be put on after being lightly pressed for 1h ~ 2h after being stacked.

In order to improve work efficiency, the final folding is best done in the transverse direction (direction of the flow).

(4) Lamination processing Lamination processing of synthetic paper is the same as lamination processing of ordinary paper. Except for thermal lamination, all other lamination processing is applicable to synthetic paper.

â‘  Dry lamination is mainly used for laminating synthetic paper and non-liquid-absorbing materials, such as synthetic paper and synthetic paper, synthetic paper and plastic film, synthetic paper and aluminum foil, etc. It should be noted that the selected adhesive should be suitable for the characteristics of the laminated material.

â‘¡Wet lamination is mainly used for lamination of synthetic paper and liquid-absorbing materials, such as lamination of synthetic paper and ordinary paper. When laminating synthetic paper and plywood, a device for laminating paper and plywood may be used, and the adhesive may be a water-based adhesive such as vinyl acetate.

â‘¢ Extruded composite synthetic paper can be used for extrusion composite of low-density polyethylene, or plastic interlayer composite with polyethylene (synthetic paper and paper, cellophane, plastic film and other materials), or it can be easily in the same conditions as OPP film Under compound. Synthetic paper can also be laminated in other ways, such as stamping lamination, wax processing lamination, hot flat lamination, etc. When laminating with heat, care should be taken to avoid the shrinkage of synthetic paper as much as possible. This is due to the high temperature during hot pressing and the slow cooling when the pressure is released, so the temperature and pressure should be controlled.

(5) Bonding process

Synthetic paper has good adhesion, so it is possible to make pasteable stamps, paste various synthetic paper bags, cartons, etc. There are various forms of bonding process, but due to the non-absorbent characteristics of synthetic paper, it brings certain difficulties to bonding. In order to improve workability, it is best to use solvent-based adhesives, and the effects of hot-melt, heat-sensitive, and pressure-sensitive adhesives are also good.

However, in actual production, most of the bonding process uses water-soluble adhesives and equipment. But this often requires the development and modification of the adhesive equipment used.

(6) Hot processing

Compared with ordinary natural fiber paper, the biggest feature of synthetic paper is its thermal processing performance. Compared with the plastic film used as the raw material, due to the addition of a large amount of inorganic filler in the paper-making process, the thermal processing performance is slightly worse.

The composition and production method of synthetic paper are basically similar to 0PP film, and its thermal processing performance is not as good as OPP film, but there are many products produced by thermal processing of synthetic paper.

â‘  Hot-melt bonding of heat-sealed synthetic paper and synthetic paper. Its appearance is characterized by the translucency of the bonded part. The adaptability of synthetic paper to several main heat sealing methods is introduced as follows.

a. Hot-plate sealing of simple synthetic paper is not suitable, but it can be used for sealing of synthetic paper with a plastic film or a heat-sealing layer.
b. Pulse sealing has good sealing strength, but the appearance of the sealing seam is poor and the efficiency is low, so it is not widely used.
c. The hot-melt cut seal has low sealing strength and is not practical. But synthetic paper is paper that can be sealed by hot melt. The method is to first compound polyethylene or polypropylene on synthetic paper, so that the synthetic paper obtains the hot-melt adhesive strength of polyethylene or polypropylene.
d. High-frequency sealing is not suitable for synthetic paper, but synthetic paper with PVC film can use high-frequency heat sealing.
C. Ultrasonic sealing can be applied, but the efficiency is not high, only for special occasions.

â‘¡Heat setting processing (vacuum forming processing) Because synthetic paper is difficult to obtain a shape with a clear outline and poor workability, it is not suitable for heat setting processing. The only synthetic papers used in this processing method are PS, PVC, and unstretched PP.

(7) Other processing

â‘  When embossing is used for embossing, roller heating or infrared heating can be used. If the synthetic paper is preheated, the embossing speed can be increased. The form of the embossing roll can use the combination of the engraving roll and paper roll for ordinary paper, or the combination of the engraving roll and rubber roll for PVC film. But compared to the two, the former is more applicable.

â‘¡When using gravure grade synthetic paper for coating, various coating processes can be performed in almost all cases without the need for an adhesive layer. Examples of coating of synthetic paper include pigment coating, pressure-sensitive adhesive coating, heat-sensitive adhesive coating, silicone coating, diazo coating, magnetic coating, wax coating, and vinylidene chloride coating. Cloth and paint coating (including post-coating and pre-coating).

â‘¢ Vacuum coating is vacuum-plated on synthetic paper to obtain a special appearance that is difficult for other materials to use as packaging materials. In addition, with different types of synthetic paper coating, you can get different styles of packaging materials.

â‘£ Other synthetic papers can be processed through perforation, die cutting, porous punching, etc. However, it is important to pay attention to the setting of the blade gap during porous punching. Generally, there is no problem in the horizontal direction, but the vertical gap must be less than 1mm, otherwise it will cause the risk of poor tearing.

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